Project ID



Low-external-input cropping systems were compared to conventional practices over several years with contrasting weather conditions. The results offer several potential options for farmers in times of rising fossil fuel costs. Diversified low-external input systems consistently outperform conventional systems on a number of important measures.

Key Question

How can Iowa farmers produce sufficient amounts of food and farm income while protecting environmental quality?


This project compared the agronomic, ecological and economic performance characteristics of three cropping systems: a conventionally managed corn-soybean rotation and two more diverse rotations (corn-soybean-oat/red clover and corn-soybean-oat/alfalfa-alfalfa) receiving much smaller quantities of nitrogen fertilizer and herbicides. Measurements included crop yields, weed dry matter production, weed seed densities in soil, economic costs and returns, fossil energy use, and soil organic matter concentrations. The experiment has been in place since 2001; this project covered the years 2007-2010.

Principal Investigator(s)

Matt Liebman


Craig Chase, Michelle Wander

Year of Grant Completion